Cytoskeleton Flashcards
intro+microtubule
main F: structure- support the structure of cells + to stay interconnected with the cell membrane + ensuring mechanical stability of cell+ maintain the junction between cells.
movement –cell motility : movement within and of the cell + move chromosomes during mitosis using mitotic spindle- Has microtubules
Microtubules- polarized by hollow cylinders, 25 nm. subunits = alpha and beta tubulin. They’re around 54 kilodaltons
-alpha + beta = dimers (polarized by magnesium and GTP to make one longitudinal protofilament.) 13 of those protofilaments In parallel arrangement=microtubule wall.
Polarization = mtoc, (microtubule organizing center) at + end. - end at periphery for depolarization (shortening of the microtubules)
- alpha-tubulin only bind to your GTP for polarization
- beta bind GDP (depolarization) +GTP
- growth occurs polarization > depolarization+ vise versa: Making it dynamically unstable
- highly dependent on maps, (microt-associated proteins) Ca, Mg and tubulin concentrations. - protein motors: ATP driven. transport the cellular components (organelles, your vesicles) Kinesins: -to +(periphery- MTOC) Dynein- retrograde mov: + to -
Microt+ cilia more stable than mitotic spindle, (more short-lived)
- most dominant MTOC is in the cilia and basal bodies and the centrosome
centrosome 0.2 um diameter and 0.3 to 0.5 um in length.
- each centrosome has two centrioles, each centriole 9 microtubules arranged in triplets
- found near nucleus (needed at replication, during mitosis. Centrioles duplicated+ cleaved, migrate to periphery of the cell. (for the migration of the chromosomes to occur = the microtubule spindles.)
Cilia - motile processes covered by cell membrane. highly organized microtubule core. F: motility of cell+sweep fluid along surface of cell sheet
One cilia= non-motile (uterine) more than one =motile (epithelia).
- composed in 9 + 2 arrangement, so nine microt+ 2 central.
- peripheral microt joined by NEXILS. microtubules to the central sheath( has 2 central pairs) connected in RADIAL SPOKES
- At the base of each cilia or flagella = basal body. orientation is similar to centriole= Triplets of the microtubules. F: motility, sensation +Cell cycle progression+ controls assembly of axoneme (structure form core of cilia+flagellum)
Flagellum (same as cilia, except longer + in bacteria and sperm cells. one flagellum while Cilia can be one/many
microfilaments
Acting Fil- thin fil, 6-8 nm. Composed of globular G actin monomers, organized in a double Helix of F actin filament.
The G actin added to pre-existing filaments or formed from pool of g-actin using nucleation factors. Such as FORMIN. (also used for actin branching where produce branching points along the microfilament to promote growth of new actin)
- G actin known to be concentrated around the cell cortex.
actin filaments are thinner and more flexible compared to microtubules. They are both polymerized.
- highly dynamic : to increase size of monomers, added to plus end (barbed end), needs to hydrolyze ATP -on the minus end, the monomers disassociate. both processes causes migration of subunits through polymer called Treadmilling- proteins associated=PROFILIN and COFILIN
in skeletal muscle, actin filaments integrated with thick myosin filaments.
- contraction of cytoplasm leads to shortening of cells or retracting cellular extensions.
- Muscle contraction caused by stretching of anti-parallel stress fibers. actin is oriented in these parallel bundles called stress fibers.
associated to cytokinesis. actin filaments associated with myosin 2; constriction results in cleavage of cells leading to cytokinesis.
- Myosin 1, involved in changing the shape of the cell during endocytosis, exocytosis and cell locomotion.
- Associated with several cytoplasmic organelles vesicles, granules and melanocytes. play role in action moving cytoplasmic components.
F:
1) cortical web supports cell membrane + maintains the shape. Web attached to proteins :SPECTRIN + DYSTROPHIN. 2) anchored in a zonula adherens+ focal adhesions. It supports microvilli and stereocilia: forms contractile bundles or stress fibers+ contractual ring in cytokinesis.
3) Works with myosin motoric protein for transportation and (Extension of cell processes exhibits small protrusion called filopodia on the surface.)
actin binding proteins affect the filament +myosin protein motor
- protein motor stores around 12 classes, the head (No binding site for acting, has ATPase) and there’s also a neck and a tail. Movement towards the positive end (where it increases in size). Only protein myosin 6 goes the opposite way.
the actin binding proteins:
actin-bundling proteins: purpose is create actin fil bundles, thicker structure for supporting and providing rigidity for cell: VILLIN.+ FIMBRIN +ALPHA ACTININ
crosslinking proteins: (similar to actin-bundling proteins) create interconnected fibers, so not really about a thicker structure. Uses FILAMIN
actin filament severing: use gelsolin to cut to shorter segments
actin capping proteins: block the sites (at ends) that help regulate the shape and size of the filament.
actin branching: associated to FORMIN. Produce branching points along the whole filament to promote growth of acting.
anchor proteins : use SPECTRIN to anchor the actin filament to membrane or other cytoskeletal structures.
Intermediate filaments
most mechanically firm +stable. size is between actin + microtubules, 10 nm. proteins of each subunit for the intermediate filaments are diverse and specific to a particular cell type of tissue.
two helical monomers twist around each other = coiled dimer. then twists around with another coiled dimer that twist around each other in anti-parallel fashion= tetramer. the ends bind together to form the free ends of an IF . Lastly, tetramer is polymerized to form IF.
F: 1) Intermediate filaments don’t disappear, and reform during cell division. (speaks to its function-structural role)
2) anchored in your desmosomes your hemidesmosomes + 3) bind actin to the cortical web.
different types of IF:
1)cytokeratin or KERATIN- in epithelial cells. composed of acidic +basic isoforms= heterodimer subunits of IF. forms outer layer that protects + strengthens tissue against any operation and helps prevent water loss. (why in epidermis). form bundle= TONAL FIBRILS- attach to junctions between epithelial cells. (play a role in epidermis, nails. Hooves, horns and scales and also feathers.)
2) VIMENTIN filament ( mesenchymal origins-Schwann cells.) junqueira mentions it as proteins: DESMIN ( smooth muscle tissue as well as Z discs in your cardiac+ skeletal muscle). Also GLIAL (assoc w GFAP- glial fibrillary acidic proteins in astrocytes)
3) NEUROFILAMENT- heterodimers form subunits for neurons
4) LAMIN- specific network in inner membrane of the nucleus (forms your nuclear lamina). has a family of 7 isoforms.
5) FILENSIN- compose cell fibres of lens. has long repeating units = spectrin-like repeats (within lens fibre cells). provides mechanical support to maintain the shape of the lens.
cell cycle
cell cycle: self-regulated sequence of events that controls cell growth and cell division.
Interphase:
- G1: prepares nutrients for DNA replication. contain DNA damage check-point+restriction checkpoint
- S1: chromosome replication initiated at replicons (S DNA damage point)
- G2: period of cell growth and organelle reorganization before cell division.
Two checkpoints monitor DNA quality during G2 phase: G2 DNA-damage checkpoint + Unreplicated-DNA checkpoint ensures DNA synthesis is complete before the cell progresses into the M phase.
Mitosis includes karyokinesis (separate f chromosome into two identical nuclei) and cytokinesis + lasts 1h.
The M-phase: spindle-assembly checkpoint and chromosome-segregation checkpoint.
Separation of two identical daughter cells concludes the M-phase.
Malfunction of cell cycle checkpoints -> mitotic catastrophe, cell death, and tumor cell development.
Apoptosis is a type of programmed cell death: intrinsic (activated by intracellular signals when cells are stressed+ releases cytochrome c from mitochondria.) and extrinsic (extracellular ligands binding to cell-surface death receptors forms death-inducing signalling complex DISC).
mitosis
process of chromosome segregation and nuclear division followed by cell division produces two daughter cells with the same chromosome number + DNA content as the
parent cell.
- Prophase: Replicated chromosomes condense and become visible (chromosome = two sister chromatids held together by a centromere). Nuclear envelope begins to disintegrate into small transport vesicles in late prophase/prometaphase. Nucleolus disappears. Kinetochore protein complex appears on each chromatid opposite to the centromere. Protein complexes that form kinetochores are attached to satellite DNA (specific repetitive DNA sequences). Microtubules of the developing mitotic spindle attach to the kinetochores and thus to chromosomes.
- Metaphase marked by the organization of the mitotic spindle, consisting of microtubules, around the MTOCs located at opposite poles of the cell. Kinetochore microtubules capture kinetochores and pull them toward MTOC, with each kinetochore capable of binding between 30 and 40 microtubules to each chromatid.
Kinetochore microtubules and associated motor proteins direct the movement of the chromosomes to the equatorial or metaphase plate.
- Anaphase begins with the initial separation of sister chromatids as cohesins holding them together break down.
Chromatids are pulled to opposite poles of the cell by molecular motors (dyneins) sliding along the kinetochore microtubules toward the MTOC.
- Telophase: nuclear envelope reforms, chromosomes uncoil, nucleoli reappear, cytoplasm divides
Cytokinesis: begins with furrowing of plasma membrane, achieved by a contractile ring of actin and myosin II filaments
Daughter cells: genetically identical with same kind and number of chromosomes, (2d) in DNA content and (2n) in chromosome number.
meiosis
Meiosis consists of two successive mitotic divisions without an additional S phase.
S phase: DNA replication= sister chromatids joined at the centromere. DNA 4d but chromosome the same 2d
M I: reductional division, reducing the chromosome number from diploid (2n) to haploid (1n)+dna 4d->2d
M II: equatorial division= two haploid daughter cells with one copy of each chromosome.
- P 1: Homologous chromosomes pair up for genetic recombination.
leptotene: Chromatin condenses, chromosomes appear, and sister chromatids become connected. Homologous pairing begins.
Zygotene: Synapsis starts and continues through pachytene. Cross ties are formed by transverse filaments binding scaffold material of both homologous.
Pachytene: Synapsis is complete, and crossing-over occurs early in this phase.
Diplotene: Chromosomes further condense, homologous chromosomes begin to separate, and chiasmata appear (junctions). Sister chromatids stay together.
Diakinesis: Homologous chromosomes condense, the nucleolus disappears, and the nuclear envelope disintegrates. - M1: homo chromosomes aligned at equitoral plate held by chiasmata which are cleaved+chromsome separate.
- A1+T1: sister chromatids remain together (held by centrosome+cohesin process. segregation+ random assortment of materal+paternal chromosomes to pole. cytoplasm divide
MII:
Cohesion complexes between sister chromatids are cleaved by a proteinase enzyme. Sister chromatids separate during A II and move to opposite poles of the cell.
The stages in meiosis II are essentially the same as those in mitosis, but haploid 1n chromosome +daughter cells with only haploid DNA content (1d).
